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Overriding reflex arc

Ben Tristem news at tristem.net
Mon Jun 4 12:39:37 EST 2001


I found this:

  "But do "reflexes" exist even physiologically? Grace points out that
sensorimotor reflex arcs exist ANATOMICALLY. But are they functionally
separate from ascending and descending sensorimotor tracts? That is, do they
exist PHYSIOLOGICALLY? Even in "simple" actions we know there is preparatory
tuning from cortex and subcortex down to spinal motor areas. As soon as you
get that, it seems to me that the notion of a functionally separate spinal
reflex is no longer justifiable.
Again, I think we are confusing terms with the situation under which they
are applied. There is no question that a reflex arc exists anatomically AND
physiologically, as can be readily demonstrated by the extremely rapid
withdrawal of the hand from a painful stimulus; this response not only does
not require conscious intervention, it occurs too rapidly for the stimulus
to even reach the brain. However, as with practically all neurally-mediated
conditions (including heart rate and blood pressure in individuals practiced
to regulate such normally "automatic" things), there is always the
possibility for descending "over-ride," such as volitionally conditioning
yourself that you will not withdraw from the stimulus. In this case, the
reflex arc is still present, but it is being volitionally suppressed. Under
such conditions, are we still dealing with a reflex, or have we now moved
into the realm of a consciously controlled event? "

here: http://www.phil.vt.edu/ASSC/newman/grace4.html






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